JPH0798411A - Optical compensation film - Google Patents

Abstract

PURPOSE:To provide the optical compensation film capable of greatly improving the coloration and visual angle characteristic of a liquid crystal display device and obviating the unequal coloration and unequal contrast thereof. CONSTITUTION:This optical compensation film is a film produced by installing an oriented film on an optically isotropic film and forming a layer contg. a liquid crystal thereon. The variation within the film plane of the Re value expressed by equation Re=¦ne-no¦Xd is within 3.0% in standard deviation. In the equation, ne denotes the refractive index in an optical axis direction; no denotes the refractive index in a direction perpendicular to the optical axis and (d) denotes the thickness (nm) of the layer contg. the liquid crystal.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a novel optical compensation film.

[0002]

2. Description of the Related Art Liquid crystal display devices have many features such as low voltage and low power consumption, which can be directly connected to an IC circuit, various display functions, and weight reduction. It is widely used as a display device for word processors and personal computers. Among them, a twisted nematic liquid crystal display device (hereinafter STN-LCD) having a twist angle of liquid crystal molecules of 160 ° or more has a larger capacity than a conventional twisted nematic liquid crystal display device (TN-LCD) having a twist angle of 90 °. Since it is capable of high speed response and is excellent in high-speed response, it is currently the mainstream of liquid crystal display devices.

However, the STN-LCD has a problem that the displayed image is colored in blue or yellow (blue mode or yellow mode). For this reason, the contrast and visibility are low in black and white display, and colorization is extremely difficult. there were. So to compensate for this coloring,
A two-layer liquid crystal black-and-white or color display using a reverse twisted STN liquid crystal cell has been proposed. However, since a plurality of liquid crystal cells are used, the weight and volume of the display device increase, or the cost increases. There is another problem that the viewing angle characteristic is deteriorated such that the contrast sharply decreases with a slight change in the viewing angle or the background color changes.

In order to solve this problem, Japanese Patent Laid-Open No. 63-
No. 167303, No. 63-167304, No. 63-1
89804, 63-261302, 63-14.
9624, JP-A-1-201607 and 1-201.
608, 1-105217, JP-A-2-2853.
No. 03, No. 2-59702, No. 2-24406, No. 2-146002, No. 2-257103, JP-A-3.
-23404, 3-126012, 3-181.
As described in Japanese Patent Publication No. 905, No. 3-194503, etc., a method of using a retardation plate instead of the reverse twist STN liquid crystal has been proposed.

According to these methods, the coloring of the STN-LCD is significantly improved, the weight and volume of the display device itself is significantly reduced, and the cost is reduced, but the STN-LCD is reduced.
The viewing angle characteristics of were hardly improved.

Therefore, in order to improve this viewing angle characteristic,
JP-A-2-285303 and JP-A-2-160204
No. EP-0482620A2, JP-A-5-15791.
Japanese Patent Laid-Open No. 1-1990 proposes a method of producing a birefringent film having a refractive index in the thickness direction larger than that in at least one direction in the film plane and using the birefringent film as a retardation plate. According to this method, the change in contrast depending on the viewing angle is reduced, and the viewing angle characteristics are improved, but the effect is still small and the manufacturing process is complicated, so it is necessary to increase the productivity and reduce the cost. is there.

Further, JP-A-2-256023, JP-A-3-141303, JP-A-3-14122, and JP-A-3-24.
In Japanese Patent No. 502, there has been proposed a method in which one film each having positive and negative intrinsic birefringence or a laminated film is used as a retardation plate. According to this method, the birefringence of the two films can be adjusted according to the characteristics of the liquid crystal cell, so the viewing angle characteristics can be improved more precisely, but two or more separately prepared birefringent films are used. Things are necessary, and the cost is high. In addition, JP-A-4-5
Japanese Patent Laid-Open No. 1101 discloses a method for improving the viewing angle problem by using only a film having a negative intrinsic birefringence value as a retardation plate.

These methods of controlling the refractive index in the thickness direction can greatly improve the viewing angle characteristics, but the contrast when viewed from the front cannot be said to be sufficiently high, and there is room for improvement. . On the other hand, JP-A-3-9325
No. 3, No. 3-9326 and No. 5-53104, No. 5-
Nos. 53016 and 5-61039 disclose that a liquid crystalline polymer is placed on a support base and used as a retardation plate. This improves the contrast when viewed from the front, but has problems such as uneven coloring and uneven contrast.

STN-LC using these birefringence modes
Since D has steep electro-optical characteristics, a large-capacity display can be obtained by time-division driving with a simple matrix electrode structure without active elements (thin film transistors or diodes). However, the response speed is slow (several hundreds of milliseconds) and gradation display is difficult, and the display performance of liquid crystal display devices (TFT-LCD, MIM-LCD, etc.) using active devices is exceeded. Absent.

For the TFT-LCD and MIM-LCD, a twisted nematic liquid crystal display device (TN-LCD) of optical rotation mode in which the alignment state of liquid crystal molecules is twisted by 90 ° is used. This display method is the most effective method as compared with other LCDs because it has a high response speed (several tens of milliseconds), can easily obtain a monochrome display, and has a high display contrast. However, since the twisted nematic liquid crystal is used, there is a problem in view angle characteristics that the display color and the display contrast change depending on the viewing direction due to the principle of the display system, and the display performance of the CRT cannot be exceeded.

Japanese Patent Laid-Open Nos. 4-229828 and 4-2.
As disclosed in Japanese Patent No. 58923, a method has been proposed in which a viewing angle is increased by disposing a retardation plate between a pair of polarizing plates and a TN type liquid crystal cell.

Further, in JP-A-4-366808 and JP-A-4-366809, a liquid crystal cell containing a chiral nematic liquid crystal having an inclined optical axis is used as a retardation plate.
Although the viewing angle is improved, the cost is high due to the two-layer liquid crystal system, which is very heavy. On the other hand, Japanese Patent Application Laid-Open No. 5-80323 proposes a method of using a retardation plate having an optical axis inclined with respect to a liquid crystal cell. However, since uniaxial polycarbonate is sliced and used obliquely, There is a problem that it is difficult to obtain a large area retarder at low cost.

That is, STN-LCD or TN
-Regarding the retardation plate used for improving the viewing angle characteristics of LCD, when it is a stretched plastic film, in order to eliminate coloring unevenness and uneven contrast due to the viewing angle in the LCD, JP-A-2-59703 and JP-A-2-59703 have the same description. Two
No. 89007, etc., it is disclosed that variations in the retardation value in the retardation plate are suppressed by optimizing the stretching conditions.

On the other hand, a liquid crystal such as a retardation plate in which a layer containing a liquid crystalline polymer is provided on the support described above, or a retardation plate in which a layer containing an alignment film and liquid crystal is provided on a support described later is used. Regarding the retardation plate used, the LCD using the retardation plate still suffers from problems such as uneven coloring and uneven contrast depending on the viewing angle.

The variation in the retardation value in the retardation plate made of the stretched plastic film is mainly due to the thickness unevenness of the retardation plate, and the thickness is uniform depending on the stretching conditions described above. And stretch it so that
It was possible to suppress the unevenness of the section. On the other hand, in the case of a retardation plate having a liquid crystal layer on a support, the present situation is that even if the thickness of the liquid crystal layer is uniform, the unevenness of the retardation cannot be suppressed.

[0016]

An object of the present invention is to provide a liquid crystal display device (L
It is an object of the present invention to provide an optical compensation film capable of improving coloring unevenness and contrast unevenness depending on the viewing angle in CD).

[0017]

[Means for Solving the Problems] The above problems are (1) a film in which an alignment film is provided on an optically isotropic film, and a layer containing a liquid crystal is formed on the alignment film. The optical compensation film, wherein the variation in Re value in the plane of the film is within 10% as a standard deviation. Formula (1) Re = | ne-no | × d ne: Refractive index in the optical axis direction no: Refractive index in the direction perpendicular to the optical axis d: Thickness of layer containing liquid crystal (nm) (2) High liquid crystal The optical compensation film as described in (1) above, which is a molecular liquid crystal. (3) The optical compensation film as described in (1) above, wherein the liquid crystal is a low molecular weight liquid crystal. (4) The optical compensation film as described in (3) above, wherein the low molecular weight liquid crystal is a discotic liquid crystal. (5) The optical compensation film as described in (4) above, which is a negative uniaxial optically anisotropic substance and has an optical axis inclined at an angle of 5 to 50 degrees from the normal line direction of the film. (6) The orientation parameter of the optically isotropic film is 0.
01 or less, and the thickness variation in the plane of the film is 5
The optical compensation film as described in (1) above, wherein the optical compensation film has a thickness within μm. (7) When forming a layer containing a liquid crystal on an alignment film, it is aged at a temperature not lower than the liquid crystal transition point of the liquid crystal but not higher than the isotropic phase transition point, and the optical compensation according to the above (1). Achieved by film.

The optically isotropic film of the present invention preferably has good light transmittance and is sold under the trade names of Zeonex (Nippon Zeon), ARTON (Nippon Synthetic Rubber), Fujitac (Fuji Film) and the like. A support formed of a material having a small intrinsic birefringence value is preferable. However, even a material having a large intrinsic birefringence value such as polycarbonate, polyarylate, or polysulfone can be preferably used if the orientation parameter is 0.01 or less during film formation. The orientation parameter is 0.0
The solvent casting method is suitable for adjusting the ratio to 1 or less. In the solvent casting method, various factors that promote orientation in the film manufacturing process are removed, and the orientation parameter is 0.01.
The following films can be manufactured. Next, the alignment film of the present invention is
A metal vapor-deposited film or a film obtained by rubbing a specific organic polymer film is used, but the present invention is not limited to this, and any known film can be used. When a discotic liquid crystal is used in the present invention, It is preferable to use an oblique alignment film.

The oblique alignment film in the present invention means that liquid crystal molecules are neither perpendicular nor parallel to the alignment film surface, and 0 <Θ <90.
This is a thin film that can be oriented by inclining at an angle Θ with a certain angle, and corresponds to a metal oblique deposition film or an alignment film obtained by rubbing a specific organic polymer film.

A typical example of the metal oblique vapor deposition film is a SiO oblique vapor deposition film, which is a method for forming a fixed substrate type as shown in FIG. 1 and a continuous vapor deposition type on a flexible substrate (film) as shown in FIG. Both forming methods can be used. The continuous vapor deposition type makes it easier to obtain a uniform film, and the manufacturing cost is significantly lower. By this oblique vapor deposition, rod-shaped vapor deposition particles grow from the substrate surface toward the vapor deposition source, but the discotic liquid crystal is oriented according to the direction of the vapor deposition particle column.

A typical organic alignment film is a fluorinated polyimide film. The angle of oblique orientation can be adjusted by applying fluorinated polyamic acid (for example, LQ1800 manufactured by Hitachi Chemical Co., Ltd.) to the substrate surface, firing at 200 to 300 ° C., and rubbing. Other materials include polystyrene derivatives.

The liquid crystal of the present invention may be a high molecular liquid crystal or a low molecular liquid crystal. The polymer liquid crystal is not particularly limited,
A cholesteric liquid crystal or a polymer liquid crystal in which a discotic liquid crystal described later is introduced in the main chain or side chain is preferable.

The low-molecular liquid crystal is preferably a discotic liquid crystal, but is not particularly limited, and is a Schiff liquid crystal, an azoxy liquid crystal, a cyanobiphenyl liquid crystal, a cyanophenylcyclohexane liquid crystal, a cyanophenyl ester liquid crystal, a benzoic acid phenyl ester. It is also possible to use low-molecular liquid crystals such as liquid crystals, cyclohexanecarboxylic acid phenyl ester liquid crystals, phenylpyrimidine liquid crystals, and phenyldioxane liquid crystals.

The discotic liquid crystal of the present invention itself has an optically negative uniaxial property, and including this discotic liquid crystal, its optical axis is oblique from the normal direction, preferably 5 to 50 degrees from the normal direction. The tilted optical anisotropic body is
It is effective for improving the viewing angle characteristics of the TN type liquid crystal cell. Also, since the structure of the discotic liquid crystal phase is kept stable below the discotic liquid crystal phase / solid phase transition temperature by orienting with a SiO oblique vapor deposition film or the like, this optical anisotropic body is also thermally stable. .

The discotic liquid crystal in the present invention is as listed below, but is not particularly limited to the following substances.

[0026]

[Chemical 1]

[0027]

[Chemical 2]

[0028]

[Chemical 3]

[0029]

[Chemical 4]

[0030]

[Chemical 5]

[0031]

[Chemical 6]

[0032]

[Chemical 7]

The orientation parameter is 0.01 or less,
In a retardation plate in which an alignment film is provided on an optically isotropic film having a thickness variation of 5 μm or less and a layer containing liquid crystal is further provided thereon, the retardation value of the retardation value in the retardation plate is increased. When the variation was within 3.0% in standard deviation, the coloring unevenness and the contrast unevenness when the film was incorporated as a retardation plate of a liquid crystal display could not be visually confirmed regardless of the viewing angle.

The present invention and examples will be described in detail below.

Example Preparation of Optical Compensation Film (KH-1) Methylene chloride solution of polyether sulfone (1
5 wt%) was cast on a steel drum, continuously stripped while suppressing stretching, and dried to obtain a film having a thickness of 50 μm. Diagonal vapor deposition was performed on this film as SiO and a vapor deposition material. At this time, the film transport speed is 10 m /
min, evaporation source temperature 1800 K, minimum vapor deposition angle 70 °. Further, a 1 wt% solution of the above-mentioned discotic liquid crystal TE-13 in methylene chloride was applied onto the deposited film, dried, and heat-treated at 220 ° C.
A 0.5 μm thick discotic liquid crystal alignment layer was formed to prepare an optical compensation film (KH-1).

Preparation of Optical Compensation Film (KH-2) Optical Compensation Film (KH-2) in the same manner as (KH-1), except that a 50 μm thick film of polyether sulfone (melt extruded product) was used as the base. Was produced.

Preparation of Optical Compensation Film (KH-3) (KH-) except that the heat treatment temperature of the liquid crystal is 140 ° C.
An optical compensation film (KH-3) was produced in the same manner as in 1).

Preparation of Optical Compensation Film (KH-4) Polyethersulfone methylene chloride solution (1
5 wt%) was cast on a steel drum, continuously stripped while suppressing stretching, and dried to obtain a film having a thickness of 50 μm. A polyimide alignment film was formed on this film and rubbed in one direction. At this time, rubbing was performed in one direction while applying a weight of about 50 g / cm ² using a cotton flock. Further, a 1,1,2,2-tetrachloroethane solution (15 wt%) of a liquid crystalline polymer shown below is applied on the alignment film, dried, and heat-treated at 190 ° C.
A liquid crystal alignment layer having a thickness of 1.1 μm was formed to prepare an optical compensation film (KH-4).

[0038]

[Chemical 8]

Preparation of Optical Compensation Film (KH-5) Optical compensation film (KH-5) except that it was based on a 50 μ thick film of polyethersulfone (melt extruded product).
An optical compensation film (KH-4) was produced in the same manner as in H-5).

Preparation of Optical Compensation Film (KH-6) (KH-) except that the heat treatment temperature of the liquid crystal is 90 ° C.
An optical compensation film (KH-6) was produced in the same manner as in 1).

Evaluation of variation in Re value of optical compensation film
The sampling method for measuring the valence Re value is 10 cm.
20 points or more were measured in the area of × 10 cm at substantially equal intervals in the vertical and horizontal directions. For the measurement, the Shimadzu Corporation ellip meter (AE
P-100) was used.

Evaluation of Contrast Unevenness on LCD [Compensation of TFT-LCD] TN type liquid crystal cell having a product of the difference in refractive index between extraordinary light and ordinary light of liquid crystal and the gap size of the liquid crystal cell at 480 nm and a twist angle of 90 degrees. The optical compensation films (KH-1), (KH-2), and (KH-3) obtained in Examples and Comparative Examples were mounted on the liquid crystal cell, and the angle dependence of the contrast in a 30 Hz rectangular wave of 0 V to 5 V with respect to the liquid crystal cell. The sex was measured by LCD-5000 manufactured by Otsuka Electronics. The position with a contrast ratio of 5 was defined as the viewing angle, and the viewing angles in the vertical and horizontal directions were obtained. Further, the uneven contrast and the uneven color were evaluated by sensory evaluation. The directions of the polarization axis of the polarizing plate of the TN liquid crystal cell, the rubbing axis of the liquid crystal cell, and the optical axis of the optical compensation sheet in this measurement are shown in FIG. [Compensation of STN-LCD] A commercially available liquid crystal display was disassembled, and optical compensation films (KH-4) and (KH-) obtained in Examples and Comparative Examples were used instead of the existing birefringent film.
Using 5) and (KH-6) as retardation plates, the optical axis was configured so that the contrast when viewed from the front was maximized, and a liquid crystal panel for a monochrome display was produced. The vertical and horizontal viewing angles at which the contrast ratio of the obtained liquid crystal panel in the driven state and the non-driven state was 5: 1 or more were obtained. Further, the uneven contrast and the uneven color were evaluated by sensory evaluation. The results are summarized in Table 1.

[0043]

[Table 1]

As is clear from Table 1, in the LCD provided with the optical compensation sheet of the present invention, the viewing angle characteristics are remarkably improved and there is no contrast unevenness or color unevenness.

[Brief description of drawings]

FIG. 1 is a diagram showing a fixed-base metal oblique vapor deposition method.

FIG. 2 is a diagram showing a continuous metal oblique deposition method on a flexible substrate.

FIG. 3 is a diagram showing a relationship among a polarization axis of a polarizing plate, a rubbing axis of a liquid crystal cell, and an optical axis of an optical compensation sheet when measuring a viewing angle characteristic in an example.

[Explanation of symbols]

 α1: Vapor deposition angle in fixed substrate metal vapor deposition method α2: Vapor deposition angle in continuous metal vapor deposition method T: Crucible containing vapor deposition material

Claims (7)

[Claims] 1. A film in which an alignment film is provided on an optically isotropic film, and a layer containing a liquid crystal is formed on the alignment film, which has a Re value represented by the following formula (1) in the plane of the film. An optical compensation film, wherein the variation is within 3.0% in standard deviation. Formula (1) Re = | ne-no | × d ne: Refractive index in the optical axis direction no: Refractive index in the direction perpendicular to the optical axis d: Film thickness (nm) 2. The optical compensation film according to claim 1, wherein the liquid crystal is a polymer liquid crystal. 3. The optical compensation film according to claim 1, wherein the liquid crystal is a low molecular weight liquid crystal. 4. The optical compensation film according to claim 3, wherein the low-molecular liquid crystal is a discotic liquid crystal. 5. The optical compensation film according to claim 4, wherein the optical compensation film is a negative uniaxial optically anisotropic substance, and the optical axis is inclined at an angle of 5 to 50 degrees from the normal line direction of the film. 6. The optical compensation film according to claim 1, wherein the orientation parameter of the optically isotropic film is 0.01 or less, and the variation in the thickness within the film plane is within 5 μm. 7. The optical element according to claim 1, wherein when the layer containing liquid crystal is formed on the alignment film, it is aged at a temperature not lower than the liquid crystal transition point of the liquid crystal and not higher than the isotropic phase transition point. Compensation film.